Figure 1.

Typical I-V curves recorded with different bias sweep ranges. The black, red, and green curves are recorded for an individual WO3 nanowire at room temperature in vacuum with 1, 3, and 5 V, respectively. Inset in
the upper left corner is a SEM image of the WO3 nanowire device. Inset in the lower right corner shows the I-V curves recorded within a small sweep range after large positive and negative bias
excursion. Inset in the upper right and lower left corner are schematic diagrams showing
the movement of positively charged oxygen vacancies.